Controlling the ACIS FP Temperature:

1

• Controlling the ACIS FP Temperature
• Turning off the DH Heater During Perigee Passages
  with Rear Sun Orientations
• Turning Off the DH Heater During a Forward Sun
  Orientation
• ACIS Ops Team

2
What Are We Asking For Today ?
Change to Standard Operations

• turn off the DH heater for all perigee passages
  for which the pitch angle is larger than 140
  degrees starting in the JAN0708 week

New Proposed Test

• turn off the DH heater for an entire perigee
  passage at forward Sun attitude OR during a
  series of calibration observations of E0102 at
  forward Sun in FEB0408 week

Success Criteria

• The Camera Body side A (1CBAT) -72.2 C and
  side B (1CBBT) -72.2 C for the duration of the
  test

3
Results of the 18 Nov 2007 Test
Cool ACIS DH for an Entire Perigee Passage
DePasquale (SAO), Vogrin (NGST) predicts a
steady state temperature of -69 to -71 C at the
HRC position and pitch angle of 150
Begin
End
4
Results of the 18 Nov 2007 Test
Cool ACIS DH for an Entire Perigee Passage
DePasquale (SAO) Side A temperature,
1CBAT Minimum temperature achieved -69.8 C
End
Begin
5
Results of the 18 Nov 2007 Test
Cool ACIS DH for an Entire Perigee Passage
DePasquale (SAO) Side B temperature,
1CBBT Minimum temperature achieved -69.8 C
End
Begin
6
Results of the 18 Nov 2007 Test
Cool ACIS DH for an Entire Perigee Passage
Begin
DePasquale (SAO) FP cooled while there was
significant Earth in the ACIS radiator FOV and
the Camera Body was cooling and the FP cooled
rapidly to -119.7 C after the perigee passage
End
7
Summary of DH Cooling Tests
Minimum Temperatures and Fit Results
8
Summary of Entire Perigee DH Cooling Test

• 1CBAT and 1CBBT reached a minimum temperature of
  -69.8 C
• no evidence that the primary survival heater
  turned on
• appears unlikely that the ACIS Camera Body can
  cool below -69.8 C if the DH heater is off for
  the entire perigee passage, the SIM is at HRC-S,
  and the pitch angle is 150 degrees
• based on this, ACIS Ops considers it safe to
  turn off the DH heater for all perigee passages
  as long as the pitch angle is greater than 140

9
What is Needed to Implement this in the JAN0708
Load ?

• New MP guideline which describes when the
  commands to turn off and turn back on the DH side
  B heater can be inserted for a given perigee
  passage
• Modification to the ACIS load review SW to check
  that the pitch angle during perigee is larger
  than 140 degrees for at least 55 ks during the
  perigee passage
• Engineering directives written to the OC/CC
  informing them of the times when the Dh heater is
  off and to expect off-nominal 1CBABT
  temperatures
• GRETA, ACIS Ops SOT MTA limits modified for
  1CBABT to a Red Low value of -74.0 C
• Contingency CAP developed and approved (CAP
  1053) to turn on the DH side B heater in the case
  that SCS 107 has run and stopped the loads before
  the heater is turned on and in the case that
  1CBAT lt -72.2 C
• plan is to turn off the DH heater for all
  perigee passages which satisfy these criteria,
  hopefully leading up to the day that the DH
  heater can be turned off at all times

10
Detector Housing Survival Heater Geometry
Trinh(NGST)

• HR7, HR8 22 W _at_ 29 V
• Prime survival -71.1 C
• Rdnt survival -73.6 C
• Better than 1.19 C accuracy (_at_ -70 C ) for
  1YA94 SSTS that controls survival heater
• Located on Z face of Detector Housing (side A,
  1CBAT)
• Closest telemetry thermistor is 1CBAT (FM07)

11
New Test Turn Off the DH side B Heater in a
Forward Sun Orientation

• Vogrins model predicts that the Forward Sun
  orientation is a colder orientation for the ACIS
  Camera Body and DH
• It is possible the Camera Body will get colder
  than -69.8 C in a forward Sun orientation
• two possibilities in February 2007, one is a
  group of E0102 calibration observations (80 ks
  at a pitch of 65.1 degrees) in the FEB0408 week
  and the other is perhaps a perigee passage at
  forward pitch
• Scenario would be very similar to the 18
  November 2007 DH cooling test, we would ask for
  additional COMs to monitor the Camera Body
  temperatures more frequently and would have CAP
  1053 ready to run to turn on the heater in the
  case that 1CBAT lt -72.2 C

12
Possible Outcomes

• 1CBAT gt -72.2 C - conclude it is safe to turn
  off the DH side B heater in forward Sun
  orientations
• 1CBAT lt -72.2 C - turn the DH side B heater back
  on and investigate why the primary survival
  heater did not turn on as expected

13
Telemetry Verification
Camera Body temperature 1CBAT/1CBBT digitization
is 2.47 C

1CBABT
-71.1 C, primary survival heater set point
-73.8 C, secondary survival heater set point
-76.0 C, must not drop below

• side A (1CBAT) cools faster than side B (1CBBT)
• side B (1CBBT) warms faster than side A when the
  DH heater is used
• side A (1CBAT) should warm faster when the
  survival heater is used

14
Turn the DH Heater Off for Future Perigee Passages

• Keeping the Camera Body colder will keep the FP
  temperature colder
• If the proposed test is successful, we want to
  turn off the DH heater for all perigee passages
  for which the pitch angle is greater than 140
  degrees

Limit Changes
Mnemonic Current Yellow Low New Yellow
Low Current Red Low New Red Low 1CBABT -70.5
C -70.5 C -75.5 C -74.0 C Camera Body
Temp 1DAHBCU 0.80 A 0.0 A 0.20 A 0.0 A
DA Htr Current B 1DAHBVO 10.5 V 0.0 V 3.5
V 0.0 V DA Htr Voltage
B 1DAHHBVO 25.0 V 0.0 V N/A/ N/A
DA Htr Input Voltage B 1DAHTBEN Enb N/A

DA Htr B
Enb/Dis 1DAHTBON On N/A

DA Htr B On/Off